Does pyo3 automatically release GIL if py is not used or do you have to do this manually?

[rafales]

Quick question. I've been looking at code of a python package. Code is fairly simple and it's here:

https://github.com/mgd020/mjml-python/blob/master/src/lib.rs

One thing I don't understand about PyO3: given that mjml2html doesn't hold any references to Python - will this code run without GIL or do you need to call allow_threads explicitly in mjml2html?

[adamreichold]

The linked code with hold the GIL for the whole duration of the call. If you want to release it, you to do so manually by calling allow_threads.

(We are working an a function attribute #[pyo3(allow_threads)] in #3610 to do this automatically, but that code is neither merged nor released yet.)